The Collaborative Natural History Study (NHS) - a combined retrospective-prospective study deaing with the Natural History of Ventricular Septal Defect (VSD), Valvar Aortic Stenosis (AS) and Valvar Pulmonary Stenosis (PS) - started in 1964. (Denver has been studying the three groups since July 1958.) The six participating institutions and the coordinating center have now completed the collection of all admission data of 2,372 patients who entered into the study. Follow-up data was collected until September 30, 1973. Standardization and quality control of the methods applied has been achieved. A number of preliminary analyses have been carried out, but these will need up-dating and reviwed during this final period of preparation of papers, reports, manuscripts etc.